Should I believe something if and only if it's true? Many philosophers have objected to this kind of truth norm, on the grounds that it's not the case that one ought to believe all the truths. For example, some truths are too complex to believe; others are too trivial to be worth believing. Philosophers who defend truth norms often respond to this problem by reformulating truth norms in ways that do not entail that one ought to believe all the truths. Many of these attempts at reformulation, I'll argue, have been missteps. A number of these different reformulations are incapable of carrying out a central role a truth norm is meant to play, that of explaining justification. The truth norm I'll defend, however, avoids the implausible results of a prescription to believe all the truths, but doesn't thereby fail to explain justification. This norm, introduced (but not defended) by Conor McHugh, states that if one has some doxastic attitude about p – i.e. if one believes, disbelieves, or suspends judgement about whether p –then one ought to believe that p if and only if p is true.